If $x \circledcirc y = 2x^{2}-y^{2}$ and $x \oslash y = 3x+y$, find $4 \oslash (2 \circledcirc -1)$.
First, find $2 \circledcirc -1$ $ 2 \circledcirc -1 = 2(2^{2})-(-1)^{2}$ $ \hphantom{2 \circledcirc -1} = 7$ Now, find $4 \oslash 7$ $ 4 \oslash 7 = (3)(4)+7$ $ \hphantom{4 \oslash 7} = 19$.